1. Field of the Invention
The present invention relates to a divider and a combiner in a communication system, and more particularly to a power divider and a combiner in a Wireless Local Area Network (‘WLAN’) system.
2. Description of the Related Art
Generally, a WLAN is a data communication system that is substituted for a conventional wired LAN and allows for exchange of data by means of a radio frequency (‘RF’) signals, even without a wired network. That is, WLANs provide all advantages and functions of the conventional LAN technology, such as an Ethernet or a token ring, without being restrained by a wired network.
A WLAN includes a plurality of access points (‘APs’) connected to a network by a wire and a plurality of stations connected to the AP wirelessly. The WLAN and the stations use the RF signal as a transmission medium. Accordingly, when a station frequently moves or a wire installation is difficult, the WLAN may be usefully utilized.
The WLAN employs a Carrier Sense Multiple Access/Collisions Avoidance (‘CSMA/CA’) scheme as a protocol of a Media Access Control (MAC) layer. The CSMA/CA scheme is obtained by modifying a Carrier Sense Multiple Access/Collisions Detection (‘CSMA/CD’) scheme used in a wired LAN in accordance with the characteristics of the WLAN. In the CSMA/CD scheme, any station may transmit data regardless of sequence, data collision on a channel is detected, and data are retransmitted when data collision occurs. In contrast, in the CSMA/CA scheme, a station confirms whether or not a channel through which data are to be transmitted is being used, and the station transmits data when the channel is in an idle state. However, when the channel is being used, the station confirms availability of the channel at a preset time and then transmits data. Since the CSMA/CA scheme has no additional control message and a simple operation process as compared with the CSMA/CD scheme, the CSMA/CA scheme may be easily achieved. Therefore, the CSMA/CA scheme is being used in a WLAN system.
In consideration of the characteristics of an RF signal, the RF signal used in such a WLAN cannot penetrate a wall in a building having a steel frame structure. Further, a shift phenomenon may occur in which the frequency band of the RF signal changes due to the presence of a wall.
FIG. 1 is a view showing a general example in which a conventional WLAN AP is installed inside a steel frame building.
Referring to FIG. 1, the inside of the building is partitioned by walls 113, 115. Herein, the AP 101 and some of stations 107, 109 and 111 do not communicate with each other via an RF signal due to the presence of walls 113, 115, respectively. Therefore, since service is not provided to some of stations 107, 109 and 111, but is provided to stations 103, 105, 107, 109 and 111, a service shadow area can be said to occur.
A method for solving the aforementioned problem includes using an RF cable, a divider and a horn antenna.
FIG. 2 is a view showing a wall-embedded type antenna system for indoor wireless communication. Referring to FIG. 2, the apparatus includes a plurality of antennas 201, 203 and 205, a divider 207 connected to the antennas 201, 203 and 205 via RF cables 211, 213 and 215, and an AP 209 connected to the divider 207 via an RF cable. In the apparatus, since the antennas 201, 203 and 205 are connected to the AP 209 by wire, interference between adjacent channels does not occur. A description on the above method has been in detail written in Korean patent application 10-2002-0062921. The system described in this application also must use the aforementioned CSMA/CA scheme. In order for the prior application to use the CSMA/CA scheme, when a station belonging to the service coverage of the first antenna 201 transmits data, stations belonging to the service coverages of the second and the third antenna 203 and 205 must have knowledge of the state of each channel. However, for instance, when a multi-direction divider is not used and the station belonging to the service coverage of the first antenna 201 transmits data to the AP 209, the stations belonging to the service coverages of the second and the third antenna 203 and 205 recognize that a channel is in an idle state and can simultaneously transmit data. Herein, since signals inputted to the second antenna 203 and the third antenna 205 are simultaneously transmitted to the AP 209 through the RF cables, data disruption can occur. Such an anomaly is called a hidden node problem. However, since it has been considered that the divider 207 only distributes power from the AP 209 to the antennas 201, 203 and 205, the divider 207 cannot be applied to the CSMA/CA scheme.
In order to solve the above-described problem, a divider is very important. A divider generally used includes a T junction divider, a resistive power divider and a Wilkinson power divider.
FIG. 3 is a view showing a conventional T junction divider. The T junction divider is a simple divider manufactured by dividing a line. Since the T junction divider can distribute power in omni-directions through ports 301, 303 and 305, the T junction divider can be applied to the system using the CSMA/CA scheme. However, since resistors are not used in lines 307, 309 and 311, the T junction divider has no loss of input power. However, since impedance matching in all ports is impossible, loss due to power reflection occurs.
FIG. 4 is a circuit diagram showing a resistive power divider. The resistive power divider is manufactured by coupling resistive elements 407, 409 and 411 to ports 401, 403 and 405, respectively. In the resistive power divider, the loss of input power occurs due to the resistive elements 407, 409 and 411. However, a desired power distribution ratio can be obtained and matching can be accomplished in all ports. Further, the resistive power divider can distribute power in omni-directions just as the T junction divider. However, since it is difficult to obtain the values of the resistive elements in an RF band or a micro frequency band and each resistive element is connected in serial to each port, a greater amount of power load is required. FIG. 5 is a circuit diagram showing a conventional Wilkinson power divider. The Wilkinson power divider is a power divider mainly used in an RF band or a micro frequency band. The Wilkinson power divider includes an input port 501, outputs ports 503 and 505, quarter wave microstrip lines 507 and 509 for port matching, and a balance resistor 511. The Wilkinson power divider uses the balance resistor 511 for port matching in an odd mode. Further, the Wilkinson power divider includes the balance resistor 511 for port matching in the odd mode connected in parallel to a power distribution port, the Wilkinson power divider has a high frequency characteristic and a power characteristic superior to those of the resistive power divider. However, in such a Wilkinson power divider, isolation is formed between the power distribution outputs ports 503 and 505 due to the balance resistor 511 used for port matching in the odd mode. Therefore, the Wilkinson power divider has an asymmetric characteristic. Consequently, since power is distributed in only one direction, it is difficult for the Wilkinson power divider to employ the CSMA/CA scheme.